I bought a new Cobra 23' Razor at xmas time. I love the boat and the new engine, except for the black residue that is left on my white transom at the end of the day. I have tried different gas brands and octanes to no avail.I have contacted Mercruiser and they say that they have no fix at this time. Cobra has done all the can including installing a new K&N filter. I have taled to Hallet boaters, Eliminator, and Essex. All have the same complaint to some level or another. If this really is a problem for the 496 Mag and the 496 Mag HO, I think we need to all get on their butts to get this problem fixed. I didn't spend all that money on a performance motor that is going to leave my boat a mess everytime my family and I go to the river. Please respond if you have had the same issue. Thanks